Chemical Properties and Electronic Structure of Molybdenum Oxysulfide Films for Advanced Photoelectrocatalysts for Hydrogen Production

— The effect of sulfur and oxygen concentrations on the formation of chemical bonds in films based on the ternary Mo–S–O compound has been studied. The compound is of interest with respect to the creation of efficient thin-film catalysts for electrochemical and, especially, photoactivated water splitting reaction. The films have been created by pulsed laser deposition in a mixture of gases (argon and oxygen) at room temperature of the substrate. The factors that greatly affect the position of the Fermi level in the band gap of the triple compound have been determined, which is mainly responsible for the choice of components in hybrid and heterostructures for photoelectrodes. The change in the chemical state of Mo–S–O films in the electrochemical process of hydrogen production in an acidic solution has been investigated. Indicators of changes in the local packing of atoms (self-organization) have been revealed: they consist in a decrease in the concentration of metal oxide clusters and an increase in the concentration of Mo–S clusters on the surface of the films. According to the thermodynamic analysis performed using the density functional theory, when oxygen is removed from the surface of Mo–S–O films, and, consequently, a hybrid MoS x /(Mo–S–O) structure is formed, the efficiency of hydrogen formation can be controlled by the quantum-chemical interaction of various clusters. Here, only certain combinations of clusters can provide sufficiently high catalytic activity.